1. Field of the Invention
The present invention relates to a safety belt system, especially for vehicles, and includes a three-point safety belt, a self-locking belt winding mechanism which is mounted to a structural part of the vehicle, and, also disposed on a structural part of the vehicle, a clamping mechanism for the belt, which clamping mechanism has at least one movable clamping jaw.
2. Description of the Prior Art
With safety belt systems having a three-point safety belt and a self-locking belt winding mechanism for preventing the belt from being withdrawn any further, there generally exists in the event of an accident the following problem: When an accident occurs, the belt is customarily arrested in the belt winding mechanism, i.e. at a location which is relatively far from that section of the belt which contacts the body of the person who is strapped in. As a result, a relatively long length of the belt exists between the arresting location and that section of the belt which extends over the person. In addition to the slack which results when the belt is put on, and in addition to the stretching of the belt which results in the vicinity of the body of the person, the stretching of the belt which results under the influence of the forces occurring during an accident produce an elongation of the belt.
A further belt elongation results from the so-called feed-roll effect in the belt winding mechanism; this is explained by the fact that the more or less tight windings of the belt, which is wound by the winding spring on the pertaining shaft, could actually be wound considerably tighter with the use of appropriate forces, so that when wound normally, a strong pull on the belt must result in a tightening of the previously undertaken belt winding accompanied by a simultaneous release of a corresponding length of the belt.
Taken altogether, there is thus produced a considerable elongation of the belt, which in the event of an accident permits a preliminary shifting of the strapped-in body, thus endangering the person who is thus strapped in.
As one solution of this problem, German Offenlegungsschrift No. 25 40 302 discloses a safety belt system of the aforementioned general type, according to which the upper mounting or guide fitting for the belt is at the same time equipped with a clamping mechanism which clamps the belt when appropriate tension is exerted thereon, thus preventing the belt from sliding further through the fitting. In this manner, there can be reduced the consequences of the feed-roll effect which occurs in the belt winding mechanism, as well as the elongation of the belt in the region between the belt winding mechanism and the guide fitting, which elongation otherwise occurs upon failure of a clamping mechanism.
However, the following drawback is characteristic of this heretofore known proposal: Since the clamping action of the clamping mechanism of the known safety belt system is activated only in cooperation with the arresting of the belt winding mechanism, at the time point that the clamping action is initiated the belt has generally already slipped through the clamping mechanism and the guide fitting due to the necessary reaction time in the self-locking belt winding mechanism. As a result, the slack in the belt at the body of the person who is strapped in is increased even more, thus enhancing shifting of the person and endangering the latter.
To eliminate this drawback, it was proposed, in German Offenlegungsschrift No. 30 40 667, to dispense with the belt clamping mechanism and in place thereof provide a tightening mechanism which engages the shaft of the belt winding mechanism and turns the latter in the event of an accident counter to the direction in which the belt is moved for withdrawal of the same from the belt winding mechanism; in this way, the belt is wound onto the winding shaft and hence tightened, at the same time eliminating the feed-roll effect.
However, there is associated with this heretofore known mechanism the drawback that on the one hand the belt slack at the body of the strapped-in person can at most be only slightly eliminated, because the tightening and the winding forces for overcoming the friction of the belt at the point where it is reversed as well as at the body of the strapped-in person are hardly sufficient, and that on the other hand after the belt has been tightened and the belt winding mechanism has been arrested, an elongation of the safety belt still occurs due to the stretching of the belt as a result of the load which is encountered.
It is therefore an object of the present invention to improve a safety belt system of the aforementioned general type in such a way that while eliminating the belt slack at the body of the strapped-in person, at the same time the belt elongation is reduced to such an extent that a preliminary shifting of the strapped-in person is extensively precluded.